In fluidized-bed jet milling, a flow consisting of a fluid and solid particles suspended in the fluid is generated in a fluidized bed such that the solid particles are reduced in size by the exchange of energy. Part of the flow containing solid particles below a certain mass or a certain weight is diverted in a sifter and fed for further processing, e.g., in a filter, while solid particles above the above-mentioned limit value remain in the residual flow and repeatedly subjected to the fluidized-bed milling until their mass or weight drops below the limit value.
The flow in the fluidized bed is facilitated during fluidized-bed jet milling by fluid jets which are introduced with high energy into the fluidized bed and induce the solid particles in the fluidized bed to engage in increased exchange of energy. This effect is achieved especially well if the high-energy fluid jets are also a suspension consisting of fluid and solid particles, were optionally removed from the fluidized bed, have experienced an increase in energy and are then returned with their increased energy into the fluidized bed.
Several measures have already been proposed to apply this principle in practice especially well.
One of these proposals is based on the discovery that the high-energy gas jets take up solid particles from the fluidized bed on entry into the fluidized bed, so that a disintegration of the particles takes place within the high-energy fluid jets, this disintegration of particles taking place especially effectively when the particle distribution in the high-energy gas jet is influenced such as to bring about the most uniform distribution possible of the particles over the cross section of the jet.
What was deliberately ignored in all these solutions is the circumstance that upon entry into the fluidized bed, not only do the high-energy gas jets bring about an exchange of energy between the solid particles of the fluidized bed and/or of the high-energy fluid jets, but this exchange of energy begins only at a certain distance from the entry of high-energy fluid jets into the fluidized bed, because the high-energy fluid jets first displace at least the solid particles into the fluidized bed as relatively laminar flows before swirling takes place, which leads to the intended exchange of energy.
The present invention deals precisely with this phenomenon by showing how the high-energy fluid jets can be introduced into the fluidized bed and how the solid particles to be disintegrated can nevertheless be prevented from being displaced at first into the fluidized bed without appreciable exchange of energy; in other words, the solid particles of the fluidized bed shall be kept in the area of the entry of the high-energy fluid jets into the fluidized bed despite the fluid jets introduced into the fluidized bed with high energy, so that the exchange of energy between the solid particles in the fluidized bed takes place reliably and very intensely in the immediate area of the entry of the high-energy fluid jets into the fluidized bed.
The essence of the present invention for accomplishing this object is, on the one hand, that centrifugal forces are caused to act on the solid particles in the area of entry of the high-energy fluid jets into the fluidized bed such that the exchange of energy between the solid particles that become parts of the high-energy fluid jets begins immediately after the penetration of the high-energy jets into the fluidized bed and, on the other hand, that the concentration of the solid particles within the fluid jets is generally improved.
The present invention will be explained in greater detail below on the basis of the drawings, which show, however, only exemplary embodiments, which do not represent any limitation of the essential features of the present invention.